2015 Fire Season
Let's begin with a comparison of this year to 2015. For those new to the area, 2015 was an extremely active fire season burning over 1 million acres across Washington State. That year featured a very low snow pack, a record hot June for many areas, and a dry summer. This primed the land for several large fires when dry lightning and windy weather entered the region in August. To put that year in perspective, here are acres burned by year since 1970 for our region which includes most of Central and Eastern Washington and the North Idaho Panhandle.
 |
| Number of acres burned each year since 1970 in Spokane Fire Area which includes most of Central and Eastern Washington and the Idaho Panhandle. |
So while over a million acres burned in Washington State, our region (most of Central and Eastern Washington and north Idaho) was hit especially hard with over 900,000 acres burned. We can also see from this graph that we have had several active fire seasons since 2012.
2019 versus 2015
With some folks comparing this year to 2015, we need to look at some comparison maps of where we stand now compared to 2015. Shown below are images from April 1st when snow pack typically peaks. First image is 2019 and then 2015.
 |
| April 1st, 2019 SWE % of Normal |
 |
| April 1st, 2015 SWE % of normal |
As one can see in 2015, snow pack was in far worse shape on April 1st. What does our current snow pack look like as of May 9th compared to around this same time in 2015?
 |
| May 9, 2019 SWE % of normal |
 |
| May 11th, 2015 SWE % of normal. |
Our snow pack in 2015 was again far worse compared to this year.
What about precipitation?
 |
Conditions are actually drier this year compared to 2015 over the Cascades, northern Washington, and the Idaho Panhandle and wetter over parts of the Columbia Basin and SE Washington. But is has been exceptionally dry over the past 30 days over most of the region as noted below.
Does low snow pack and dry winter/spring mean a bad fire year?
Let's tie this all together. Does a below normal snow pack and a dry winter/spring mean another bad fire season? Not necessarily. We did a correlation to number of acres burned each season since 1970 and compared it to several factors including April 1st snow pack, October-May precipitation, number of lightning caused fires, and late spring/summer temperatures.
The most important factor is May-August temperatures followed by number of lightning caused fires. This makes sense as a hotter summer typically brings dry conditions and makes the grass and timber readily available to burn. But still this correlation by itself isn't very high as number of acres burned depends how many times a critical fire weather pattern sets up as hot temperatures won't start fire by itself. 2015 is a prime example as that season wasn't exceptionally busy locally until August 10th when the critical pattern set up with dry lightning and several rounds of wind. The fires that had a start date between Aug 11-25 consumed 834,623 acres. It is worth noting that mountain snow pack on April 1st has a very low correlation and amount of winter/spring precipitation has nearly 0 correlation to number of acres burned during fire season. So this summer we will be closely monitoring summer temperatures and watching critical fire weather patterns.
Pattern change
The dry weather over the past 30 days will result in elevated chances for fire spread this weekend as the winds begin to increase on Sunday (May 12th). The pattern looks to change towards the end of next week with wetter than normal conditions favored May 16-20th.
 |
| Climate Prediction Center 6-10 day precipitation outlook valid May 16-20, 2019 |
Summer/Fire Outlook
So since summer weather ultimately decides what kind of fire season we'll have based on the local study mentioned above, what can we expect? Let's begin with temperatures. No surprise here with elevated odds of warmer than normal.
 |
| CPC June-August 2019 Temperature Outlook issued April 18th, 2019 |
Why is this no surprise? Because our summers have been trending warmer at each location since 1900 as shown below.
 |
| Summer (June-August) temperature trends since 1900 as plotted from the OWSC Trend Analysis Tool |
The big red circles show a significant warming trend, while the smaller red circles also show warming, but the trend is considered insignificant in terms of long term trends. The plot above as well as the few that follow can be generated from the Office of Washington State Climatologist Trend Analysis tool found here
Below is a graph showing average temperatures in Spokane since 1900. The past four summers are highlighted in red and have been noticeably warm.
What about precipitation this summer? The summer's of late have been quite dry, especially in Spokane as shown below.
The past four summers (June-August) in Spokane have brought less than 1.00" of precipitation, something that hasn't been accomplished for more than two consecutive summers since 1900 until now. Normal June-August precipitation is 2.48". Will we make it five in a row? Let's see what the Climate Prediction Center is saying.
 |
| CPC June-August 2019 Precipitation Outlook issued April 18th, 2019 |
Slightly elevated odds of wetter than normal conditions for SE Washington into the Idaho Panhandle with Equal Chances elsewhere. What kind of pattern would result in this?
 |
| NMME Forecast issued early May of precipitation anomalies June-August 2019 |
The pattern would be high pressure off the coast deflecting systems into Alaska and down into Eastern WA/N Idaho and the Northern Rockies as the NMME (National Multi-Model Ensemble) shows. This could give Eastern WA/N Idaho periods of cooler and showery conditions. But getting this pattern nailed months in advance is nearly impossible for the models to get right. That area of high pressure could set up further east over our region giving hot/dry weather. Or it could set up slightly further west providing occasional rounds of cool/wet weather. There is low confidence of this occurring.
Here are the official National Fire Outlooks for July and August.
 |
| National Fire Outlook issued by NIFC May 1st valid for July 2019 |
 |
| National Fire Outlook issued by NIFC May 1st valid August 2019 |
Summary
Given all the factors that came together in the 2015 fire season, 2019 is likely to not be a repeat but could still be an above normal season. The dry weather pattern as of late is expected to change in the May 16-20 period with wetter than normal conditions as well as cooler temperatures. Going into summer warmer than normal temperatures are favored while precipitation is more of a wild card. The Fire Potential Outlook for this summer favors above normal for western Washington, and the northern valleys and mountains with near normal potential elsewhere.
No comments:
Post a Comment